Many laser radar systems have been built which rely on the transmission of a high energy illuminating pulse. Most often these systems rely on solid state lasers operating in the near infrared with a lasing media of Neodymium-YAG or Erbium doped glass. Many of these systems utilize multiple pulses over a period of time to detect remote objects and improve range accuracy. These systems are often based on a single detector optical receiver. To develop a complete picture of a scene, the laser and optical receiver must be scanned over the field of view, resulting in a shifting positional relationship between objects in motion within the scene. Flash ladar systems overcome this performance shortcoming by detecting the range to all objects in the scene simultaneously upon the event of the flash of the illuminating laser pulse.
U.S. Pat. No. 3,230,527 awarded to Wehde, Wiesloch, et. al. describes an automatic landing system for a VTOL aircraft which relies on a microwave system to establish the distance to the ground station. However, this system is really a half duplex communication system or transponder, rather than a true radar altimeter, as it relies on an intelligent response from a microwave beacon at the ground station. U.S. Pat. No. 4,866,450 awarded to Chisholm describes an instrument landing system for an aircraft which also relies on a microwave transponder to establish the distance to the ground station with the improvement of a GPS based time synchronization. U.S. Pat. No. 5,593,114 awarded to Ruhl describes an automatic landing system for an aircraft which relies on a millimeter wave forward looking radar set or alternatively, a passive forward looking infrared (FLIR) imaging sensor to establish the distance and identify features on the runway. U.S. Pat. No. 5,334,848 awarded to Grimm describes an automatic docking system for a spacecraft which relies on a dual optical camera system and dichroic optical reflectors installed on the docking station.